In recent years, mobile terminal devices such as mobile handsets equipped with a ringing device for security purposes such a buzzer or an alarm are becoming popular with growing security awareness.
Conventionally, a buzzer for security purposes installed in a mobile handset is configured to be controlled by hardware. For example, a mobile handset is equipped with hardware that is capable of ringing regardless of the power on/off state of the mobile handset. This enables the ringing operation upon turning the switch of the buzzer on, even if the power of the main unit of the mobile handset is off.
However, when mounting such a security buzzer with hardware control on a mobile terminal device such as a mobile handset, there is a problem that the hardware needs to be mounted on each mobile terminal device, incurring costs such as production costs in proportion to the number of units.
Therefore, for example, Patent document 1 discloses an alarm control method with which various sounds can be created without a divider circuit and the like for switching sounds, by providing unit for specifying data for deciding the type of the alarm by a program, and unit for outputting the data bit by bit at regular intervals.
However, when providing a mobile terminal device with ringing by software control as in Patent document 1, there is a problem that while the ringing can be performed with no problem in the state in which the mobile terminal device is activated, but in the state in which the mobile terminal device is not activated (for example, in the state in which the power of the mobile terminal device is off), the buzzer cannot perform ringing. In addition, since it requires some time to activate the mobile terminal device, there is a problem that it takes time before the ringing of the buzzer actually starts after an instruction for the start of the ringing is issued by a switch and the like of the buzzer.
In relation to this technique, Patent document 2 discloses a mobile handset equipped with a security function with which even when the mobile handset is performing a process to turn off the power, the security buzzer starts ringing immediately upon turning the switch of the security buzzer on, and continues to ring.                Patent document 1: Japanese Laid-open Patent Publication No. 02-253409        Patent document 2: Japanese Laid-open Patent Publication No. 2007-082122        